Difference between public and private strings

I am implementing SNMP on our Servers and Switches, I am new to this but learning a great deal from this wonderful site.
I have read and been told to change the public and private strings (which are like passwords.)

Can someone please explain in laymans terms what exactly public and private strings, and how they would likly be used?

I am a bit rushed to get this projesct started, so I need a quick heads up and basic understanding.

public is the default community string for RO (read only), which is used for things like monitoring, reading MIB values etc...

private is the default community string for RW (read-write), which would be used to do things like push config changes.

These strings can (and most definitely should) be changegd so that the snmp management stations and the network devices use something that no one knnows about. Further, it's also best practice to restrict the source addresses from where you can make these sorts of transactions.

for instance, on a cisco router you might want something like this:

snmp-server community ThePasswordIsSecret RO 10

access-list 10 permit 192.168.33.128 0.0.0.15

This way only machines addressed within this range that know the community string can grab information about your gear.

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